Disco 1 Brake Vacuum Pump (ERR3539) Plunger Compression?

I need to replace the break pump on my discovery.

I have another pump to put on it, but id like confirmation on how hard the plunger on the pump should be to press in?

I cant get it to move at all, even with 11 stone on top of it.

Is this right - is the, i assume, spring inside it that strong?



The scrap engine the pump is off had a hot and quick end of life, but other bits of it did survive, so i may be lucky with the pump - i just dont know how hard they should be to operate by hand!

Thanks,
Julian

it is very ,you wont do it by hand

thanks for that - clears up some of the doubt i have about using the unit!

julian